U.S. patent number 4,873,708 [Application Number 07/048,236] was granted by the patent office on 1989-10-10 for digital radiographic imaging system and method therefor.
This patent grant is currently assigned to General Electric Company. Invention is credited to Dominic A. Cusano, George E. Possin.
United States Patent |
4,873,708 |
Cusano , et al. |
October 10, 1989 |
**Please see images for:
( Certificate of Correction ) ** |
Digital radiographic imaging system and method therefor
Abstract
A digital radiographic imaging system which employs co-operative
means for converting the x-rays to an optical image having enhanced
quality and detecting said optical image. The x-ray conversion
medium employed in the improved radiographic system is positioned
physically contiguous to a bi-directional array of electrical
charge transfer devices which convert the optical image to an
electronic analog representation thereof. Digital information
processing means are further included in the improved radiographic
system to convert the electronic analog representation of the
optical image to a recorded digital representation thereof. The
x-ray conversion medium being employed in the improved radiographic
system is a high efficiency scintillator body which moves
co-operatively with the photo detection means being employed in a
further synchronious relationship with a moving fan beam of X
radiation being employed to generate the desired optical image
after passage through a stationary object.
Inventors: |
Cusano; Dominic A.
(Schenectady, NY), Possin; George E. (Schenectady, NY) |
Assignee: |
General Electric Company
(Milwaukee, WI)
|
Family
ID: |
21953448 |
Appl.
No.: |
07/048,236 |
Filed: |
May 11, 1987 |
Current U.S.
Class: |
378/19; 250/580;
250/582; 327/509; 250/361R; 250/369; 250/370.09 |
Current CPC
Class: |
G01T
1/2018 (20130101); G01T 1/202 (20130101) |
Current International
Class: |
G01T
1/202 (20060101); G01T 1/20 (20060101); G01T
1/00 (20060101); G01N 023/04 () |
Field of
Search: |
;378/62,19,10,11
;250/369,361R,370.09,370.11,327.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Oldelft Publication Entitled "X-ray Image Sensor Based on an
Optical TDI-CCD Imager"..
|
Primary Examiner: Fields; Carolyn E.
Assistant Examiner: Porta; David P.
Attorney, Agent or Firm: McDevitt; John F.
Claims
What we claim as new and desire to secure by Letters Patent of the
United States is:
1. A digital radiographic image recording system which
comprises:
(a) a movable scintillator body having a dense, self-supporting and
substantially void-free single flat layer configuration which is
substantially transparent to the optical radiation emitted by said
medium, said scintillator body comprising a polycrystalline
scintillator ceramic with a high X-ray absorption value and a
material density of at least 99% so that substantially all X
radiation impinging thereon will be converted therein to optical
radiation without excessive scattering and loss of the converted
optical radiation,
(b) a stationary X-ray source to expose said scintillator body to
an X-ray fan beam moving in a linear non-arcuate travel direction
after passage through an object,
(c) a photodetection member positioned physically contiguous with
said moving scintillator body and movable therewith so that both
scintillator body and photodetection member move synchronously
together with the moving x-ray fan beam in the same linear
non-arcuate travel direction for conversion of said moving fan beam
to an optical image for simultaneous detection of said optical
image in a point-by-point and line-by-line manner,
(d) said movable photodetection member having a plurality of charge
transfer devices arranged in electrically connected columns and
rows, said columns being aligned in the same linear non-arcuate
travel direction as the moving X-ray fan beam while said rows being
aligned substantially transverse thereto in order to also
synchronously shift the signals being generated by optical
radiation impinging on the individual charge transfer device
located in the same column in the opposite travel direction to the
travel direction of said moving photodetection member and with said
synchronous signal shifting being carried out by a time delay and
integration mode of operation to form an electrical analog
representation of said optical image without experiencing
substantial optical attenuation, the pixel arrangement in said
photo-detection member also being unbroken so that all impinging
optical radiation will be collected, the synchronous signal
shifting further being carried between adjoining charge transfer
devices such that signals are shifted from a device having received
optical radiation to the next adjoining device at the same velocity
rate as the physical movement, and
(e) digital processing means for immediately converting said
electrical analog representation of said optical image to a
recorded digital representation thereof with higher quantum
detection efficiency, resolution and contrast.
2. A digital radiographic image recording system as in claim 1
wherein said time delay and integration mode of operation for said
moving photodetector member is achieved with a spatial orientation
of the individual charge transfer devices such that the individual
charge transfer devices forming a row are aligned in an offset but
overlapping positional relations with respect to the next adjoining
row of individual charge transfer devices.
3. A digital radiographic image recording system as in claim 2
wherein a like spatial relationship is maintained between all
alternate rows of individual charge transfer devices in said
photodetection member to form a parallel alignment for the column
orientation of said charge transfer devices in said photodetection
member.
4. A digital radiographic image recording system as in claim 1
wherein the charge transfer devices are charge coupled devices.
5. A digital radiographic image recording system as in claim 1
wherein the synchronized signal shifting between adjoining charge
transfer devices proceeds serially throughout each column of charge
transfer devices in said photodetector member and with the output
signals from each column being further stored in the digital
processing means of said radiographic image recording system.
6. A digital radiographic image recording system as in claim 1
which further includes visual display of the digitized
information.
7. A digital radiographic image recording system as in claim 6
wherein said visual display is operatively associated with said
means for digital recording of the optical image.
8. A digital radiographic image recording system as in claim 1
wherein said scintillator body comprises a sintered polycrystalline
rare earth doped rare earth oxide ceramic exhibiting high density,
optical clarity, and a cubic crystalline structure.
9. A digital radiographic image recording system as in claim 8
wherein said rare earth oxide is selected from the group consisting
of Gd.sub.2 O.sub.3, Y.sub.2 O.sub.3, La.sub.2 O.sub.3 and Lu.sub.2
O.sub.3.
10. A digital radiographic image recording system as in claim 9
wherein said rare earth dopant ion is selected from europium,
neodymium, ytterbium and dysprosium.
11. A digital radiographic image recording system as in claim 8
wherein said ceramic comprises between about 5 and 50 mole percent
Gd.sub.2 O.sub.3, between about 0.02 to about 12 mole percent of at
least one rare earth activator oxide selected from the group
consisting of Eu.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Yb.sub.2 O.sub.3,
Dy.sub.2 O.sub.3, Tb.sub.2 O.sub.3, and Pr.sub.2 O.sub.3, the
remainder being Y.sub.2 O.sub.3.
12. A digital radiographic image recording system as in claim 1
wherein said scintillator body comprises a composite of x-ray
stimulable phosphor crystals suspended in a matrix of a solid
synthetic organic polymer having an optical refractive index
closely matching the optical refractive index of said phosphor
crystals while also being substantially transparent to the optical
radiation being emitted by said phosphor crystals.
13. A digital radiographic image recording system as in claim 12
wherein said phosphor is barium fluorochloride activated with
europium ion and said synthetic organic polymer is a
polysulfone.
14. A digital radiographic image recording system as in claim 12
wherein the phosphor crystals occupy a minimum weight fraction in
said member of at least 50%.
15. A digital radiographic image recording system as in claim 12
wherein the polysulfone polymer is a homopolymer.
16. A digital radiographic image recording system as in claim 12
wherein said phosphor crystals comprise a europium activated barium
fluorohalide further containing a sufficient level of an impurity
ion selected from Group 1A and 3A elements in the periodic table of
elements to reduce the optical refractive index of said
phosphor.
17. A digital radiographic image recording system as in claim 16
wherein said impurity ion is incorporated as a halide compound of
the impurity element.
18. A digital radiographic image recording system as in claim 16
wherein the europium activator level is in the approximate range
from 0.1-2.0 weight percent based on the weight of said
phosphor.
19. A digital radiographic image recording system as in claim 16
wherein the level of impurity ion is in the approximate range from
0.3-3.0 weight percent based on the weight of said phosphor.
20. A digital radiographic image recording system as in claim 16
wherein the phosphor is europium activated barium
fluorochloride.
21. A method to record a digital radiographic image which
comprises:
(a) forming an optical image by scanning an object exposed to a
stationary X-ray source with a moving scintillator body in a linear
non-arcuate travel direction during exposure of said object to a
moving X-ray fan beam to form said optical image as a
point-by-point and line-by-line composite of the subject being
scanned,
(b) said scintillator body having a dense, self-supporting and
substantially void-free single flat layer configuration which is
substantially transparent to the optical radiation emitted from
said medium, said scintillator body comprising a polycrystalline
scintillator ceramic with a high X-ray absorption value and a
material density of at least 99% so that substantially all X
radiation impinging thereon will be converted therein to optical
radiation without excessive scattering and loss of the converted
optical radiation,
(c) simultaneously transmitting said optical image when formed to a
moving photodetection member aligned with said moving x-ray fan
beam and moving synchronously in the same linear non-arcuate travel
direction as said moving x-ray fan beam,
(d) said moving photodetection member being positioned physically
contiguous with said moving scintillator body and movable therewith
so that both scintillator body and photodetection member move
synchronously with the moving x-ray fan beam in the same linear
non-arcuate travel direction for conversion of said moving X-ray
fan beam to an optical image for simultaneous detection of said
optical image as an electrical analog representation thereof and
without experiencing substantial optical attenuation,
(e) said moving photodetection member also having a plurality of
charge transfer devices arranged in electrically connected columns
and rows, said columns being aligned in the same linear non-arcuate
travel direction as the moving x-ray fan beam while said rows being
aligned substantially transverse thereto in order to also
synchronously shift the signals being generated by optical
radiation impinging on an individual charge transfer device located
in the same column in the opposite direction to the travel
direction of said moving photodetection member and with said
synchronous signal shifting being carried out by a time delay and
integration mode of operation, the pixel arrangement in said
photodetection member also being unbroken so that all impinging
optical radiation will be collected, the synchronous signal
shifting further being carried out between adjoining charge
transfer devices such that signals are shifted from a device having
received optical radiation to the next adjoining device at the same
velocity as the physical movement, and
(f) immediately converting said electrical analog representation of
said optical image to a recorded digital representation thereof
with digital processing means at higher medium detection
efficiency, resolution and contrast.
22. A method as in claim 21 wherein said time delay and integration
mode of operation for said moving photodetection member is achieved
with a spatial orientation of the individual charge transfer
devices such that the individual charge transfer devices forming a
row are aligned in an offset but overlapping positional
relationship with respect to the next adjoining row of individual
charge transfer devices.
23. A method as in claim 21 wherein a like spatial relationship is
maintained between all alternate rows of individual charge transfer
devices in said photodetection member to form a parallel alignment
for the column orientation of said charge transfer devices in said
member.
24. A method as in claim 21 wherein the synchronized signal
shifting between adjoining charge transfer devices proceeds such
that signals are shifted from a device having received optical
radiation to the next adjoining device after the latter device has
received optical radiation.
25. A method as in claim 21 wherein the synchronized signal
shifting between adjoining charge transfer devices, proceeds
serially through each column of charge transfer devices in said
composite member and with the output signals from each column being
further stored by the digital processing means.
26. A method as in claim 21 wherein the signal shifting is carried
out with charge coupled devices.
27. A method as in claim 21 which further includes digital imaging
of the optical image.
28. A digital radiographic image recording system which
comprises:
(a) a movable scintillator body having a dense, self-supporting and
substantially void-free single flat layer configuration which is
substantially transparent to the optical radiation emitted by said
medium, said scintillator body comprising a polycrystalline
scintillator ceramic with a high x-ray absorption value and a
material density of at least 99% so that substantially all X
radiation impinging thereon will be converted therein to optical
radiation without excessive scattering and loss of the converted
optical radiation,
(b) a stationary X-ray source to expose said scintillator body to
an X-ray fan beam moving in a linear non-arcuate travel direction
and after passage through an object,
(c) a photodetection member positioned in direct physical contact
with said movable scintillator body and moving therewith so that
both scintillator body and photodetection member move synchronously
with the moving x-ray fan beam in the same linear non-arcuate
travel direction for conversion of said moving X-ray fan beam to an
optical image for simultaneous detection of said optical image in a
point-by-point and line-by-line manner without experiencing
substantial optical attenuation,
(d) said movable photodetection member having a plurality of charge
transfer devices arranged in electrically connected columns and
rows, said columns being aligned in the same linear non-arcuate
travel direction as the moving x-ray fan beam while said rows being
aligned substantially transverse thereto in order to synchronously
shift the signals being generated by optical radiation impinging on
the individual charge transfer devices located in the same column
in the opposite direction to the travel direction of said movable
photodetection member and with said synchronous signal shifting
being carried out by a time delay and integration mode of operation
to form an electrical analog representation of said optical image,
the pixel arrangement in said photodetection member also being
unbroken so that all impinging optical radiation will be collected,
the synchronous signal shifting further being carried out between
adjoining charge transfer devices such that signals are shifted
from a device having received optical radiation to the next
adjoining device at the same velocity rate as the physical
movement, and
(e) digital processing means for immediately converting said
electrical analog representation of said optical image to a
recorded digital representation thereof with higher quantum
detection efficiency, resolution and contrast.
29. A method to record a digital radiographic image which
comprises:
(a) forming an optical image by scanning an object exposed to a
stationary X-ray source with a moving scintillator body in a linear
non-arcuate travel direction during exposure of said object to a
moving X-ray fan beam to form said optical image as a
point-by-point and line-by-line conversion of the subject being
scanned,
(b) said scintillator body having a dense, self-supporting and
substantially void-free single flat layer configuration which is
substantially transparent to the optical radiation being emitted
from said medium, such scintillator body comprising a
polycrystalline scintillator ceramic with a high x-ray absorption
value and a material density of at least 99% so that substantially
all X radiation impinging thereon will be converted therein to
optical scintillator without excessive scattering and loss of the
converted optical radiation,
(c) simultaneously transmitting said optical image when formed to a
moving photodetection member aligned with said moving x-ray fan
beam and moving in the same linear non-arcuate travel direction as
said moving x-ray fan beam,
(d) said moving photodetection member being positioned in direct
physical contact with said moving scintillator body and movable
therewith so that both scintillator body and photodetection member
move synchronously with the moving x-ray fan beam in the same
linear non-arcuate travel direction for conversion of said moving
x-ray fan bean to an optical image for simultaneous detection of
said optical image as an electrical analog representation thereof
and without experiencing substantial optical attenuation,
(e) said moving photodetection member also having a plurality of
charge transfer devices arranged in electrically connected columns
and rows, said columns being aligned in the same linear non-arcuate
travel direction as the moving x-ray fan beam while said rows being
aligned substantially transverse thereto in order to also
synchronously shift the signals being generated by the optical
radiation impinging on an individual charge transfer device located
in the same column in the opposite direction to the travel
direction of said moving photodetection member and with said
synchronous signal shifting being carried out in a time delay and
integration mode of operation, the pixel arrangement in said
photodetection member also being unbroken so that all impinging
optical radiation will be collected, the synchronous signal
shifting further being carried out between adjoining charge
transfer devices such that signals are shifted from a device having
received optical radiation to the next adjoining device at the same
velocity rate as the physical movement, and
(f) immediately converting said electrical analog representation of
said optical image to a recorded digital representation thereof
with digital processing means at higher quantum detection
efficiency, resolution and contrast.
Description
RELATED PATENT APPLICATIONS
A co-pending application Ser. No. 07/046,443, filed May 6, 1987 now
abandoned, assigned to the same assignee as the present invention,
discloses a high efficiency type x-ray image converter member which
can be employed in practicing the present invention. Specifically,
said converter medium comprises a scintillator body having a layer
configuration and made up of x-ray stimulable phosphor particles
suspended in a substantially void-free matrix of a particular solid
organic polymer. The phosphor and polymer constituents in said
composite medium have substantially the same optical refractive
index characteristics so as to be substantially transparent to the
optical radiation being emitted by said phosphor constituent when
retrieving a latent radiographic image previously stored in said
medium. In still another co-pending application Ser. No.
07/046,442, filed May 6, 1987, now abandoned also assigned to the
present assignee, there is disclosed a like type scintillator body
wherein the phosphor composition has been modified to reduce its
optical refractive index and thereby provide a closer match to the
optical refractive index characteristics of various solid organic
polymers. More particularly, said further improved scintillator
body contains a europium activated barium fluorohalide phosphor
material modified to further include a sufficient level of an
impurity ion selected from Group 1A and 3A elements in the periodic
table of elements to reduce the optical refractive index of said
modified phosphor.
BACKGROUND OF THE INVENTION
This invention relates generally to an improved digital
radiographic imaging and recording system which is especially
useful in medical radiographic applications and more particularly
to a system of said type wherein a moving fan beam of X radiation
is employed in combination with photodetection means to digitize
and record the optical image formed immediately responsive to X
radiation.
As previously indicated, scintillator materials emit visible or
near visible radiation when stimulated by x-rays or other high
energy electromagnetic photons hence are widely employed in various
industrial or medical radiographic equipment. In medical
applications it is desirable that the scintillator output be as
large as possible to minimize exposure of the medical patient to
the x-ray dosage. A known class of scintillator materials
considered for use in computerized tomography applications is
monocrystalline inorganic compounds such as cesium iodide (CsI),
bismuth germanate (Bi.sub.4 Ge.sub.3 O.sub.2), cadium tungstate
(CdWO.sub.4), calcium tungstate (CaWO.sub.4) and sodium iodide
(NaI). Another known class of scintillator materials comprises
polycrystalline inorganic phosphors including europium activated
barium fluorochloride (BaFCl:Eu), terbium activated lanthanum
oxybromide (LaOBr:Tb), and thulium activated lanthanum oxybromide
(LaOBr:Tm). A still third class of already known scintillator
materials found useful in computerized tomography comprises various
dense sintered polycrystalline ceramics such as rare earth doped
yttria/gadolinia (Y.sub.2 O.sub.3 /Gd.sub.2 O.sub.3) and
polycrystalline forms of said previously mentioned phosphors
including BaFCl:Eu, LaOBr:Tb,CsI:Tl, CaWO.sub.4, and
CdWO.sub.4.
In U.S. Pat. No. 4,383,327, there is disclosed a scanning slit
electronic radiographic system employing a linear array of
electronic radiation detectors to digitize and record the optical
image formed in an image intensifier device when stimulated by X
radiation after passage through a medical patient. It is recognized
in said prior art disclosure that an image intensifier device is
subject to various problems of scattered radiation producing
distortion and loss of information details in the optical image
being formed. It is still further recognized in said prior art
disclosure that such radiation scattering in the image intensifier
device requires an increased exposure of the patient to radiation
in order to prevent such degradation of the image quality and which
is an undesirable consequence for medical radiographic
applications. The emerging optical image from said image
intensifier device in said prior art radiographic system is
optically focused upon remotely located charge coupled devices
forming the photodetection means in said system thereby occasioning
additional detection efficiency losses in the optical information
being retrieved such as resolution and contrast losses. The
physical orientation of charge coupled devices forming the
photodetection means in said prior are radiographic system consists
of parallel aligned columns and rows in a spaced apart
configuration. Such a spaced apart configuration creates void
spaces whereby still further optical information can be lost for an
inaccurate representation of the optical information being
retrieved.
A staggered physical orientation for said photodetection means is
disclosed for a digital radiographic system of the same type in a
publication entitled "X-ray Image Sensor Based on an Optical
TDI-CCD Imager" authored by J. deGroot, J. Holleman, and H.
Wallinga and issued by Oldelft Optical Industries. Said improved
photodetection means is reported to be physically coupled to the
exit window of an image intensifier device to provide a more
unbroken and thereby more accurate representation of the optical
information being retrieved. By further reason of the relatively
complex and fragile nature of the image intensifier device being
employed in both prior art radiographic imaging systems, however,
said devices are seen to remain stationery while being operated
with the patient being moved during exposure to the x-ray fan beam
such as positioned on a movable table aligned therewith.
Understandably, any involuntary movement of the medical patient in
either prior art radiographic imaging process creates still another
source of error, such as blurring, in the optical image being
formed.
It remains desirable, therefore, to provide an improved digital
radiographic imaging system of this general type which is not
subject to the inherent limitations experienced when using an image
intensifier device.
It is another important object of the invention to provide a more
compact and rugged as well as simplified equipment system and
method for digitally recording a radiographic image as formed and
in a manner providing improved quantum detection efficiency.
Still another important object of the present invention is to
provide such an improved digital radiographic imaging system that
is relatively inexpensive as well as more reliable to construct and
operate while further not experiencing loss in the principal
benefits now achieved with a radiographic technique of this
type.
SUMMARY OF THE INVENTION
Novel composite x-ray conversion and photodetection means have now
been discovered for a digital radiographic imaging and recording
system which provides enhanced quality for the optical image being
formed responsive thereto. More particularly, said improved
composite medium comprises a movable scintillator body having a
dense, self-supporting and substantially void-free layer
configuration which is substantially transparent to the optical
radiation emitted from said medium and which is positioned
physically contiguous to a photodetector member moving
synchronously therewith so that both scintillator body and
photodetection means are exposed to a moving x-ray fan beam in the
same linear travel direction for conversion of said moving x-ray
fan beam to an optical image for simultaneous detection of said
optical image in a point-by-point and line-by-line manner. Said
moving x-ray fan beam is generated in the present digital
radiographic imaging system with an x-ray source having a movable
scanning bar member combined therewith which includes a slit
opening and moves in a linear travel direction. The movable
photodetection member in the present digital radiographic imaging
system comprises a plurality of bi-directional charge transfer
devices arranged in electrically interconnected columns and rows,
said columns being aligned in the same linear travel direction as
the moving x-ray fan beam while said rows being aligned
substantially transverse thereto in order to also synchronously
shift the signals being generated by optical radiation impinging
upon an individual charge transfer device located in the same
column in the opposite direction to the travel direction of said
moving photodetection member and with said signal shifting being
carried out by a time delay and integration mode of operation to
form an electrical analog representation of said optical image.
Accordingly, the presently improved digital radiographic imaging
system basically comprises said movable scintillator body having a
dense self-supporting and substantially void-free layer
configuration which is substantially transparent to the optical
radiation emitted from said medium, an x-ray source to expose said
scintillator body to an x-ray fan beam moving in a linear travel
direction and after passage through an object, a photodetector
member positoned physically contiguous with said movable
scintillator body and movable therewith so that both scintillator
and photodetector member move synchronously with the moving x-ray
fan beam in the same linear travel direction for conversion of said
moving x-ray fan beam to an optical image for simultaneous
detection of said optical image in a point-by-point and
line-by-line manner, said movable photodetector member having a
plurality of bi-directional charge transfer devices arranged in
electrically connected columns and rows, said columns being aligned
in the same linear travel direction as the moving x-ray fan beam
while said rows being aligned substantially transverse thereto in
order to also synchronously shift the signals being generated by
optical radiation impinging on an individual charge transfer device
located in the same column in the opposite direction to the travel
direction of said moving photodection member and with said signal
shifting being carried out by a time delay and integration mode of
operation to form an electrical analog representation of said
optical image, and immediately converting said electrical analog
representation of said optical image to a recorded digital
representation thereof by digital processing means. In said
presently improved digital radiographic imaging and recording
system said time delay and integration mode of operation for said
moving photodetector member is achieved with a spatial orientation
of the individual charge transfer devices such that the individual
charge transfer devices forming a row are aligned in an offset but
overlapping positional relationship with respect to the next
adjoining row of individual charge transfer devices and with the
preferred embodiments maintaining a like spatial relationship
between all alternate rows of individual charge transfer devices in
said photodetector member to form a parallel alignment for the
column orientation of said charge transfer device in said
photodetector member. The preferred charge transfer devices are
charge coupled devices exhibiting the operational characteristics
hereinafter described but with already known charge injection
devices also being contemplated as capable of performing in a like
manner. As also to be described more fully hereinafter in
connection with the preferred embodiments for practicing the
invention, the synchronized signal shifting between adjoining
charge transfer devices proceeds such that signals are shifted from
a device at the same velocity as the scan movement albeit in the
opposite direction.
General operation of the above defined present radiographic imaging
and recording system comprises forming an optical image by scanning
an object with a moving scintillator body in a linear travel
direction during exposure of said object to a moving x-ray fan beam
to form said optical image as a point-by-point and line-by-line
composite of the object area being scanned, said scintillator body
having a dense, self-supporting and substantially void-free layer
configuration which is substantially transparent to the optical
radiation being emitted from said medium, simultaneously
transmitting said optical image when formed to a moving
photodetector member aligned with said moving x-ray fan beam and
moving synchronously in the same linear travel direction as said
moving x-ray fan beam, said moving photodetector member being
positioned physically contiguous with said moving scintillator body
and movable therewith so that both scintillator body and
photodetector member move synchronously with the moving x-ray fan
beam in the same linear travel direction for conversion of said
moving x-ray fan beam to an optical image for simultaneous
detection of said optical image as an electrical analog
representation thereof and without experiencing substantial optical
attenuation, said moving photodetector member also having a
plurality of bi-directional charge transfer devices arranged in
electrically connected columns and rows, said columns being aligned
in the same linear travel direction as the moving x-ray fan beam
while said rows being aligned substantially transverse thereto in
order to also synchronously shift the signals being generated by
optical radiation impinging on an individual charge transfer device
located in the same column in the opposite direction to the travel
direction of said moving photodetector member and with said signal
shifting being carried out by a time delay and integration mode of
operation, and immediately converting said electrical analog
representation of said optical image to a recorded digital
representation thereof by digital processing means. In the
preferred operating embodiments, digital computer means are
employed for recording the optical image as formed by the composite
x-ray image converter and detection means and which can further
include electronic signal processing circuitry to further enhance
the quality of the finally recorded radiographic image by various
already known information processing techniques. Accordingly, the
electronic analog signals generated by said photodetection means
employed in said preferred radiographic imaging process are
transmitted to said digital image processing means which can still
further include contemporaneous visual display operatively
associated with the digital image processing means such as a
vidicon camera or cathode ray tube. As can be noted from the
elimination of any requirement for an image intensifier device in
carrying out the above defined digital radiographic imaging and
recording process, there is achieved a higher quantum detection
efficiency, resolution and contrast in the retrieved optical image
together with an unbroken pixel array for the radiographic
information being retrieved.
To provide enhanced quality for the optical image formed in
accordance with the present invention, it is required that the
scintillator body material absorb most of the X radiation being
employed so that radiographic information details do not escape as
well as have a substantially void-free solid medium so as not to
produce excessive scattering and loss of the converted optical
radiation. Said desired x-ray conversion behavior is achieved in
the presently useful scintillator materials with a high absorption
value at a material density of at least 99% or greater to provide
superior resolution capability for the optical image generated in
accordance with the present invention.
As previously indicated, a relatively broad class of solid state
scintillator materials has been found useful as the conversion
medium in digital radiographic imaging and recording system. A
preferred general class of polycrystalline ceramic scintillator
materials deemed suitable for the present x-ray conversion medium
is disclosed in U.S. Pat. No. 4,525,628, also assigned to the
present assignee, as exhibiting superior conversion efficiency
compatible with modern computerized tomography or other digital
imaging requirements. Said general class of ceramic scintillator
materials comprises rare earth oxides doped with rare earth
activators which yield a cubic crystal structure of high density
and optical transmittance with the preferred rare earth oxides
being selected from the group consisting of Gd.sub.2 O.sub.3,
Y.sub.2 O.sub.3, La.sub.2 O.sub.3, and Lu.sub.2 O.sub.3 and wherein
the rare earth activator ion is selected from the group consisting
of europium, neodymium, ytterbium and dysprosium. Representative
ceramics further specified in said general class of superior solid
state scintillator materials include Gd.sub.2 O.sub.3 activated
with europium ion and Gd.sub.2 O.sub.3 combined with Y.sub.2
O.sub.3 which is also activated with europium ion. An entirely
dissimilar class of solid state monocrystalline scintillator
materials is also disclosed in said aforementioned reference which
can be used as the present x-ray conversion medium despite higher
costs and difficulties of preparation as well as somewhat inferior
performance characteristics. Said lesser preferred single crystals
are grown from a melt and include NaI:Tl, CaF.sub.2 :Eu, Bi.sub.4
Ge.sub.3 O.sub.2, CsI:Tl and CdWO.sub.4.
A more limited class of the above defined polycrystalline ceramic
scintillator materials which is preferred for the present x-ray
conversion medium is disclosed in U.S. Pat. No. 4,473,513, also
assigned to the present assignee. More particularly, said
scintillator body comprises a sintered polycrystalline yttria
(Y.sub.2 O.sub.3)-gadolinia (Gd.sub.2 O.sub.3) ceramic exhibiting
high density, optical clarity, uniformity and a cubic crystalline
structure which further includes one or more oxides of the rare
earth elements selected from europium, neodymium, ytterbium,
dysprosium, terbium, and praseodymium as activators along with
oxides of other metal ions selected from zirconium, thorium, and
tantalum to serve as transparency-promoting densifying agents. A
typical ceramic of said type comprises about 5 to 50 mole percent
Gd.sub.2 O.sub.3, between about 0.02 and 12 mole percent of at
least one rare earth activator oxide selected from the group
consisting of Eu.sub.2 O.sub.3, Nd.sub.2 O.sub.3, Yb.sub.2 O.sub.3,
Dy.sub.2 O.sub.3, Tb.sub.2 O.sub.3 and Pr.sub.2 O.sub.3, the
remainder being Y.sub.2 O.sub.3. Both of said above identified
commonly assigned patents are further specifically incorporated by
reference into the present application to avoid further necessity
for added description herein of a suitable medium in which to
achieve said conversion of the impinging X radiation to an optical
image having enhanced visual characteristics.
A different preferred class of scintillator materials deemed
suitable for the present x-ray conversion medium is disclosed in
the above enumerated co-pending applications. Accordingly, said
scintillator body may comprise a composite of x-ray stimulable
phosphor crystals suspended in a matrix of a solid synthetic
organic polymer having an optical refractive index closely matching
the optical refractive index of said phosphor crystals while also
being substantially transparent to the optical radiation being
emitted by said phosphor crystals. A representative x-ray converter
medium of said type is barium fluorochloride activated with
europium ion while said synthetic organic polymer is a polysulfone.
In said typical medium, the phosphor crystals occupy a minimum
weight fraction of at least 50% whereas the polysulfone polymer is
a homopolymer. A different x-ray converter medium of this same type
utilizes phosphor crystals of europium activated barium
fluorohalide further containing a sufficient level of an impurity
ion selected from Group 1A and 3A elements in the periodic table of
elements to reduce the optical refractive index of said phosphor.
In said latter medium, the europium activator level is preferrably
maintained in the range from 0.1-2.0 weight percent based on the
weight of said phosphor whereas the impurity ion level is
preferably maintained in the approximate range from 0.3-3.0 weight
percent based on the weight of said phosphor. Said phosphor
modification can be achieved as further described in said
aforementioned co-pending applications, both of which are also
specifically incorporated by reference into the present
application, by simply combining a halide compound of the impurity
element with the already formed phosphor material.
As well be illustrated below in greater detail for the hereinafter
described preferred embodiments, the digital recording of an
optical image having enhanced visual characteristics further
requires that the photodetection means operatively associated with
the present scintillator medium co-operate in a particular manner.
As previously indicated, it is essential that said co-operating
photodetection means be positioned physically contiguous to said
scintillator body so that substantially all optical radiation
emerging from the latter medium be detected and which can possibly
be most easily achieved when the individual members are joined in
direct physical abutment. As also previously indicated, the pixel
arrangement in said photodetection means is required to be unbroken
so that all of the impinging optical radiation will be collected
and which can also possibly be achieved with a staggered column
orientation of the individual detector arrays. For digitally
recording an optical image having enhanced visual quality in
accordance with the present improvement, it becomes still further
required that said photodetection means be operated so that the
optical radiation being received is processed in a controlled
manner. More particularly, the charge transfer taking place in the
electrically interconnected devices being employed in the present
photodetection means is required to be at the same rate as the
movement rate for said moving photodetection means albeit in the
opposite travel direction in order to provide proper signal
integration for each fixed frame pixel being viewed in the
stationery object being irradiated during the time scan for said
viewing process. Said proper signal integration is carried out in
the present photodetection means by controlling the synchronized
signal shifting so that signals are shifted between adjoining
interconnected charge transfer devices at the same velocity as the
scan movement albeit in the opposite travel direction. Accordingly,
the synchronized signal shifting between interconnected charge
transfer devices proceeds serially throughout each column of
devices in the photodetection means being employed and with the
output signals from each column being further collected in the
digital processing means of the present radiographic imaging and
recording system.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation partially in block diagram
form for a typical digital radiographic imaging and recording
system according to the present invention.
FIG. 2 is an exploded view depicting the scanning type composite
x-ray conversion and photodetection member being employed in the
present radiographic imaging and recording system.
FIG. 3 is a side elevation view depicting a preferred physical
orientation for the charge transfer devices being employed as the
photodetection means in the present radiographic imaging and
recording system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, FIG. 1 depicts partially in block
diagram form a typical equipment means employed to form and record
a digital radiographic image in accordance with the present
invention. A source of X radiation, such as a conventional x-ray
tube 10 is shown which is operated in the conventional manner with
a fixed coarse aperture member 12 to provide a horizontal x-ray
beam of suitable size 14 corresponding in area size to the overall
object being scanned for exposure of said selected object, such as
for a medical patient. The emerging x-ray fan beam is further
modulated with a movable scanning member 18 having a slot opening
20 to provide a moving x-ray fan beam 22 for irradiation of said
medical patient 24 in accordance with the present radiographic
imaging process. As can be noted from said drawing, the linear
travel direction 26 for said moving x-ray fan beam proceeds
upwardly although it is contemplated that an opposite travel
direction can be employed, if desired, for a second slice image and
with eventual return of said scanning member to its original
starting location. Said movable scanning member 18 is synchronously
operated with a composite x-ray conversion and photodetection
member 28 shown to be travelin the same linear travel direction 30.
As is more fully explained in connection with FIG. 2 description
for said composite x-ray conversion and photodetection member 28,
the X radiation in the moving fan beam aligned therewith is
thereafter processed synchronously in a particular manner by said
means after passage through the selected stationery object. The
output signals from said photodetection means employed in the
present radiographic system provide an electronic reproduction of
an optical image formed upon conversion of said impinging X
radiation for further processing with high speed electronic
computer means 32 operatively incorporated in the present
radiographic system. Said digital computer or processor means 32
includes an image processing algorithm developed for said purpose
to produce a digitized representation of the presently enhanced
optical image. As previously indicated, said digital processing
means 32 in the present radiographic system can also include
additional signal processing means to further enhance the quality
of said converted optical image. Said digitized optical image is
finally recorded by known electronic recording means 34 such as a
magnetic tape and which as further previously indicated can be
further contemporaneously viewed as a reconverted visual image by
other known electronic display means (not shown) operatively
associated with said recording means.
The present method of recording a digital radiographic image
thereby comprises forming an optical image by scanning an object
with a moving scintillator body in a linear travel direction during
exposure of said object to a moving x-ray fan beam to form said
optical image as a point-by-point and line-by-line composite of the
entire object area being scanned, simultaneously transmitting said
optical image when formed to a moving photodetector member aligned
with said moving x-ray fan beam and moving synchronously in the
same linear travel direction as said moving x-ray fan beam,
converting said optical image with said moving photodetector member
to an electrical analog representation thereof and without
experiencing substantial optical attenuation, and immediately
converting said electrical analog representation of said optical
image to a recorded digital representation thereof having improved
visual characteristics by digital processing means. For the purpose
of better achieving said objective it is essential that a
co-operative physical relationship be maintained in said composite
x-ray conversion and photodetector member 28 so that all of the
optical radiation being generated in said medium will be detected.
Accordingly, not only is there a requirement for said x-ray
conversion medium to be physically positioned adjacent to said
photodetection means and preferably in direct physical abutment
therewith but also that the physical geometry or configuration of
the detection elements along with proper operation of said
detection elements in said photodetection means enable capture of
all impinging optical radiation. By said latter means it now
becomes possible to provide an unbroken or complete digital
representation for all optical radiation generated in accordance
with the present radiographic imaging process.
FIG. 2 is an exploded representation depicting the individual
subcomponents or parts of the composite x-ray conversion and
photodetection member 28 suitable for use in the above described
digital radiographic imaging and recording system. More
particularly, a bar-shaped movable scintillator body 38 is depicted
as spaced apart from a contemporaneously movable bi-directional
charge transfer array 42 to form said composite member 28 when
joined together in a physically contiguous relationship. Such a
physical configuration for the composite member permits a direct
conversion of the x-rays impinging upon the scintillator body to be
converted to an optical image and be simultaneously converted to
electrical signals representative of said optical image with higher
quantum detection efficiency, resolution and contrast than would
occur if intermediate transducing steps were introduced along with
still other quantum losses and limitations inherent with the now
employed image intensifier devices. Understandably, the still
further compact, rugged and inexpensive nature of the present
composite member represents still other desirable advantages being
achieved. The drawing further depicts the physical orientation of
charge transfer devices 44 forming the photodetection means of said
composite member. Said charge transfer devices 44 are generally
aligned to columns 46 and-rows 48 for electrical interconnection
and operation in a particular manner to be described more fully
hereinafter. In such manner, said individual charge transfer
devices 44 are preferably constructed in modular form whereby
vertical and horizontal resolution elements (not shown) are
employed in an already known manner to provide the pixel photosites
for the electronic analog representation of the optical image being
recorded. It becomes thereby possible in said already known manner
to construct a typical photodetector array having said
configuration with an overall bar width of 14" or greater to scan
about 17" in a vertical direction, such as desired for medical
chest examinations, and made up of 16 electrically paired modules
physically staggered in horizontal rows of a co-operative time
delay and integration mode of operation to be more fully explained
below. Each of said typical modules can be known charge coupled
devices in the form of semi-conductor chips having a representative
50 pixel column and 128 columns per chip to provide a total 6400
pixel representations in the converted electronic image per chip.
Accordingly, when said representative photodetector array is
operated in the time delay and integration mode hereinafter
explained, there will be achieved a total pixel number of
approximately 5.times.10.sup.6 pixels being represented in the
overall image that is recorded according to the present invention.
It can be further appreciated from said illustrated method of
radiographic imaging according to the present invention that a 50
fold integration of signal takes place for each fixed frame of the
body pixel being viewed.
FIG. 3 is a side elevation view depicting the above type
representative photodetector member 42. The illustrative charge
coupled devices 44 in said detector member 42 are thereby
physically oriented in staggered vertical columns 46 with a
parallel vertical alignment being found between adjoining columns.
Said charge transfer modules 44 are further physically oriented in
rows transverse to said parallel columns with a co-operative
spatial orientation of the individual charge transfer modules in
said rows such that the individual charge transfer modules forming
a row are aligned in an offset but overlapping positional
relationship with respect to the next adjoining rows of said
individual charge transfer modules. By overlapping the detection
devices in said manner there can be achieved an unbroken pixel
representation for the object being viewed thereby capturing all of
the x-ray details made available along with an improvement in the
horizontal resolution of the recorded image being achieved. When
said representative detector array 42 is operated as further
explained below so that charge transfer takes place in the 50 pixel
columns by downward movement while the composite detector member 28
proceeds upwardly in a linear travel direction and with said upward
scan speed being controlled accurately with said downward charge
transfer it becomes possible to scan the desired overall 17" scan
distance during a typical 0.5 second scan time period at an overall
body radiation exposure of 1 mR dosage or less.
The proper signal processing in the composite x-ray conversion and
photodetection member 28 above described to achieve an enhanced
image quality according to the present invention has already been
generally recognized. More particularly, in the aforementioned U.S.
Pat. No. 4,383,327, there is employed a photodetection array being
operated in a time delay and integration mode of operation to
provide a recorded digital radiographic image and wherein the
signal processing means therein employed is analogous to that which
can be employed for proper operation of the present type composite
x-ray converter and photodetection means. Accordingly, said prior
art method of recording a digital radiographic image employs a
charge coupled device array having as an integral part thereof
signal processing capabilities whereby the signals generated by
each of the detectors are stored in respective storage elements.
These stored signals, at controlled time intervals, are all shifted
by clocking signals to the storage elements of other adjacent
detectors. Once the signals have been shifted, the signals are
augmented by new signals, if any, generated by the respective
detectors of the storage elements in which the signals are stored.
After having been shifted through several storage elements, these
augmented signals exit from the array to be further processed and
conditioned so as to enable an image to be stored or reconverted
into a visual image created through a suitable visual system. In
connection with shifting and processing of radiation signals in the
present radiographic imaging system, like synchronization is
maintained between movement of the x-ray fan beam herein employed
to form the initial optical image and the presently employed
composite conversion and detector member 28 at a controlled speed
and in a known pattern. This controlled speed is synchronized with
the control time intervals at which signals are shifted from
storage element to storage element. Specifically, the shifting
pattern that is the sequence that the signals follow as they are
shifted from storage element to storage element within the
photodetection array, is designed to be generally similar to the
movement pattern for the aforementioned moving components in the
present radiographic system. As the x-ray fan beam moves, causing
the radiation passing through the small area thereof to likewise
move and fall upon an adjacent detector element, the pixel signal
generated prior to the movement is shifted to the storage element
associated with the detector receiving the radiation at the same
velocity rate as the physical movement. In this manner, each pixel
in the accumulated image results from an integration process. The
signal processing being carried out in the present radiographic
imaging and recording system by said time delay also typically
features columns of the image sensing elements that are tied to a
vertical column analog transport register. At the top of each
vertical analog transport register is a horizontal analog transport
register. An imaging sensing element generates an electrical signal
as a function of the radiation sensed thereby and temporarily
stores said signals. These stored signals are passed along to the
column shift registers in a controlled manner when activated by a
vertical clocking signal. In this way charges are accumulated in
the vertical analog transport register for eventual transfer to the
horizontal analog transport register when activated by a horizontal
clocking signal. When the object being viewed is scanned along said
charge coupled device matrix in the same direction as the columns
and at the same rate as the charge is passed from line-to-line, a
non-blurred image results with each pixel in the accumulated image
being the result of the aforementioned described integration. In
the further description of the preferred embodiments for said prior
art radiographic imaging and recording system, there is further
described the operation of a two phase charge coupled device shift
register to carryout the desired signal processing. Accordingly,
the analogous operation of said detector devices is presented
herein as being exemplary also of proper operation for the
improvement being carried out in accordance with the present
invention.
In connection with such already known operation for said two phase
charge coupled devices as described in FIG. 3 of U.S. Pat. No.
4,383,327, two complimentory clock voltage wave forms are
respectively connected to alternate closely-spaced gate electrodes
on a surface of a thin insulating layer provided on a piece of
silcon metal. An upper layer of the silcon is n-doped. The
substrate of the silcon layer is p-doped. The first clock signal is
connected to alternately spaced gate electrodes and similarly the
second clock voltage is connected to separately spaced apart gate
electrodes. As a result of said electrical interconnection, voltage
potential wells are created by the clock voltage wave forms. That
is, a deep potential well which attracts electrons is created under
an electrode where the clock voltage is high and disappears under
an electrode where the clock voltage is low. In said manner a
finite charge of electrons or other charge bundles such as "holes"
are shifted along said two phase charge coupled device register as
controlled by the two clock signals being employed. Further
electrical interconnection between said two phase charge coupled
shift-register as controlled by the aforementioned clock signals
and the imaging sensing elements being employed in said
photodetection means enables the desired time delay and integration
mode of operation to take place. Charge coupled two-dimensional
image arrays of said type are commercially available. For example,
Fairchild Semi-Conductor, Inc. manufactures a 380.times.488 image
array suitable for carrying out the practice of the present
invention. The model number for such array is #CD221CDC with the
operation of such an array being fully detailed and understood by
those skilled in the electronic art through the specification
sheets that accompany these devices.
The above described operation for the present digital radiographic
imaging system produces the digitized final image in a
point-by-point and line-by-line manner. In typically doing so, the
moving x-ray fan bean proceeds vertically upward through a
horizontal line of pixels in the object being scanned with the
emerging X radiation impinging upon a line of photosites located in
the scintillator body portion of the moving composite x-ray
conversion and photodetection member being employed. The
point-by-point conversion of X radiation to optical photons by the
scintillator material is thereupon directly transmitted to the
individual detector elements located in the physically adjacent
photodetection array. The electronic signal generated responsive to
the optical radiation being sensed by said individual detector
element is vertically shifted downward from a first row in said
photodetection array to an adjacent row upon activation by a
vertical clock signal. At the same time interval, the composite
member continues vertical upward movement so that X radiation now
falling upon the next line of photosites located in the
scintillator body will be passing through the same line of pixels
or photosites in the object being scanned that previously fell upon
the last line of photosites. As said imaging process continues, the
electronic signals being shifted vertically downward in said
photodetection array each represent the accumulated signals
corresponding to a single pixel emerging from the object being
scanned. Thus, the individual pixels in the digitized image
ultimately produced result from an integration mode of operation
with said integration proceeding over the full length of columns in
said photodetection array. After such integration, the accumulated
signals are shifted horizontally to provide input signals to the
further operatively associated digital processing means employed in
the presently improved radiographic imaging system.
It will be apparent from the foregoing description that a broadly
useful composite x-ray conversion and photodetection means has been
discovered for digital radiography enabling enhanced quality for
the optical image being formed and recorded. It will be apparent
from said foregoing description, however, that various
modifications in the specific embodiments above described can be
made without departing from the spirit and scope of the present
invention. For example, it is contemplated that the movable
scanning member forming a movable x-ray fan beam in the present
x-ray imaging system can be provided with a different shaped
aperture to still further reduce the radiation dosage to which a
medical patient is otherwise exposed. By limiting said aperture
opening to just those physical locations being occupied by the
co-operating aligned detector elements in said composite member,
such as with properly located holes or slots, there can be achieved
such objective. It is further contemplated that charge injection
devices can be directly bonded to the scintillator body in said
composite member and thereby serve as alternate photodetection
means in the present radiographic imaging and recording system.
Additionally, a substitution of still other phosphor, ceramic and
polymeric materials other than specifically disclosed to form the
scintillator body portion of said composite member is further
deemed possible without experiencing substantial loss of the
enhanced image quality. Moreover, still other physical
configurations of the presently improved digital radiographic
imaging and recording system than above specifically disclosed are
possible so long as the essential dynamic relationships above
disclosed are preserved between the moving x-ray exposure means and
said moving composite member. It is intended to limit the present
invention, therefore, only by the scope of the following
claims:
* * * * *